well I don't know how the real military works, but the Iniative was a bunch of big-ego jerks who seemed to barely be able to do more than hold a gun imo... (it's still a wonder that they managed to capture Spike, but then again he wasn't on a very high point in his life at that time) So I'm not surprised that after the Adam debacle, they just left the facility there with the deads inside. And since it was classified (like [MENTION=9583]crazysoulless[/MENTION] said), they wouldn't have sent an entire team to recover the body. Even for Sunnydale that would have looked a little out of the ordinary.
And if I'm right in my counts, S7 was (2years 6months+6months+3months) around 3 years and 3 months after the end of S4... We're far from a decade and the bodies wouldn't have had time to desecate(sp?) completely.
(wow I watch waaaaay too many CSI and Bones episodes XD)